The existing solutions for channel feedback to enable multi-cell coordinated transmission includes: 1) Channel State Information (CSI) matrix feedback; 2) Precoding Matrix Index (PMI) feedback; and 3) uplink (UL) sounding feedback.
The above types of feedback have the following drawbacks:
(1) CSI matrix feedback leads to a large signaling overhead, although it can provide a base station (BS) with full channel information;
(2) PMI feedback is an efficient feedback mechanism in single BS transmission mode, however, in multi-cell transmission, PMI feedback may largely limit the freedom of precoding operation of involved multiple cells;
(3) UL sounding feedback is an efficient feedback approach in time division duplex (TDD) mode, but it is difficult to be applied in frequency division duplex (FDD) mode because symmetry of uplink and downlink channels is utilized. Additionally, the asymmetric interference distribution among the downlink (DL) and UL will damage the accuracy of channel information estimation.
Therefore, there is a need for an efficient method for channel state information feedback which can solve the above problems.